This invention relates to a device for mechanically adjusting an optical element, and more specifically to a device for adjusting the tilt angle of a lens or mirror and locking the position in a manner that is stable over temperature, time and environmental stresses.
An optical mount is a device that points a laser beam by controlling the orientation of an optic. In a laser system, a laser beam strikes an optic and is directed to a further point on the optical pathway by the interaction between the beam and the optic. The optical mount can be used to redirect the laser beam to another point by repositioning the optic.
There is a requirement in laser systems for very high thermal and mechanical stability in order to maintain beam quality, output power, beam divergence and mechanical boresight. Lasers are used in precision applications, such as surveying and military targeting, and in demanding environments, such as the environments in which military laser systems typically operate, have such very high stability requirements.
Ideally, enhanced stability laser systems would be designed and built with no adjustable components. With everything immovably fixed, alignment and boresight stability would depend solely on the quality of the basic design. There would be less tendency for misalignment in the field. Unfortunately, this option would lead to lasers with relatively broad tolerances and relatively poor performance. Over the years, the laser system industry has developed adjustment systems for lasers and the optical components with which they operate that result in very good laser alignment and stabilityxe2x80x94albeit at the cost of additional system complexity, increased manufacturing time for alignment of the laser system, and increased labor costs. For laser systems having high stability requirements, such as military laser systems, the additional complexity, time and alignment labor costs are significantly higher.
The use of adjustable mounting apparatus for supporting optical components in a laser system such as optical fibers, mirrors, beam splitters, lenses, gratings, and the like, is known. For example, it is frequently necessary to position a first optical element, such as a mirror, optical fiber, or waveguide relative to a second optical element, such as another mirror, optical fiber, waveguide, or beam expander microscope objective lens. Frequently, the relative positioning of such optical components must be very precise, often requiring accuracies on the order of wavelength dimensions. Even smaller allowable tolerances are anticipated in the future.
One approach to the design of precision laser system alignment mounts has been based on kinematic mounting, where three directional constraints determine the alignment. Typically, this might be accomplished with two plates, one mounted on the other at three points, the first point being a ball in socket in each of the plates, the second point being a ball in v-grooves in each plate aligned radially with the sockets, and the third point being a screw threaded through one plate and resting on the surface of the second plate on a radial line from the sockets. The plates can be held together with springs attached to their outer edges. This mechanism has a hinge point formed by the two balls. When the screw is adjusted, one plate will tilt with respect to the other and, if one plate is fixed, the edge of the second plate will be translated perpendicular to the radial line from the hinge to the adjustment screw. The difficulty with this semi-kinematic mounting mechanism is that, as additional adjustments are needed along other axes, additional alignment assemblies must be stacked, thereby increasing the size and complexity of the laser system.
Typical alignment fixtures use a pair of screws to set the alignment in one direction. One screw is used to push the alignment fixture while the other is used to pull the alignment fixture (opposing screws). When the correct alignment of the laser system has been achieved, both screws are xe2x80x9ctightenedxe2x80x9d to prevent any additional movement of the alignment fixture when the system is exposed to shock and vibration environments. Tightening the adjustment screws, however, will change the system alignment just performed unless it is exactly balanced, and detracts from the ability to make very fine alignment adjustments. Stability of such a locking system is also questionable because the stress induced in the mechanism by the screws is along the direction of adjustment. When the stress changes due to changed environmental conditions, the adjustments change as well. Achieving the exact adjustment balance is very tedious and time consuming, resulting in increased cost and time for manufacturing the laser system.
An alternative approach to locking a laser system""s alignment has been to use a single screw pushing against a stiff spring. To lock the alignment fixture after the laser system has been aligned, a nut on the single screw is tightened against the fixture. This is a variant of the two screw approach described in the paragraph above. Both of these locking schemes suffer the same problem of potentially changing the just-performed alignment setting when the locking nut tension is increased, again causing additional time and effort to be spent aligning the laser system, along with the added attendant cost. Both schemes also suffer from the same stability problem because of their reliance on the stress conditions of the interface between the adjustment screw and the mount along the direction of travel.
A variety of optical elements can be selected for use as a laser beam relay, depending upon it purpose and application. Laser system design involves a continuing struggle to balance laser performance requirements against the various operational and environmental stability requirements in which the system will operate, and to balance the ease of manufacture and alignment of the laser system against its requirements for long and short term stability in the environment where the delivered laser system will be used. The task of optically aligning the output of a laser beam is alleviated to some extent by the systems disclosed in the prior art.
In addition, U.S. Pat. No. 4,869,583 discloses a laser relay mounting assembly which receives and conducts a laser beam wherein the laser relay mounting assembly adjusts the laser output coincident with a desired axis which further describes a locking screw. U.S. Pat. No. 6,198,580 describes a gimbaled optical mount using a bearing element as a pivot point. There is an optical mount with a locking fastener disclosed in U.S. Pat. No. 6,016,230.
However, the state of the art implementations have yet to satisfy the commercial applications for an optical mounting and there is considerable room for improvement. Thus, there is a need for improved apparatus for easy alignment of optical components that provides low cross talk and enhanced locking strength. In particular, there needs to be an improved locking mechanism that does not impart forces in the angular direction. There is also a need for improved apparatus that permits fine alignment of optical components and a means for quickly locking the adjusted position of the optical element. Also, there is a need for improved apparatus that will permit aligned optical components to retain their alignment under very adverse and demanding operational and environmental conditions, such as the environments in which military laser systems operate. The locking mechanism should be strong to overcome adverse environmental conditions.
The invention is devised in the light of the problems of the prior art described herein. Accordingly it is a general object of the present invention to provide a novel and useful apparatus and technique that can solve the problems described herein. The foregoing needs are satisfied by the apparatus disclosed herein for easy mounting and alignment of optical components in such a manner that permits aligned optical components to retain their alignment under very adverse and demanding operational and environmental conditions. In addition, the mounting and alignment apparatus herein disclosed permits much finer alignment of optical components and permits faster alignment adjustment of the optical components.
In one embodiment the present invention comprises three plates coupled by live hinges that provide a two axis gimbal adjustable mount, wherein the locking mechanism sandwiches the moveable plates with a contact force perpendicular to the adjustment axes. The configuration of the present invention allows low cross talk and an environmentally stable clamp.
The mounting described herein can be used to hold optical elements that need to be angularly adjusted, such as optical fibers, mirrors, beam splitters, lenses, and gratings. In one embodiment the adjustable optical element mounting is fabricated from a solid block of material and has two live hinges formed therein by narrow cuts through most of the block of material. The axes of the two live hinges lie on radial lines that typically perpendicular (orthogonal) to each other; and the axes of the two live hinges also typically lie perpendicular (orthogonal) to the optical axis of the optical element that is fastened in the optical component mounting. The two live hinges are also oriented so that the motion of each hinge axis is uncoupled or independent from the motion of the other hinge axis.
The locking feature of this optical component mounting system clamps the adjustable elements of the mount orthogonal to the direction of their motion. The locking screw for each axis does not touch the adjustable element. Instead, the locking screw passes through a clearance hole in the adjustable element allowing the locking flexures to xe2x80x9csandwichxe2x80x9d the adjustable element. When the locking screw is not tight, the adjustable element slides between the locking elements that form the bread of the sandwich. In this way a locking mechanism is formed that does not create cross talk to the adjustable element. This facilitates speed and ease of alignment, as well as a rigid final assembly that lends itself to dimensional stability in rugged environments, such as those typically experienced in military applications.
In order to use a single screw for adjustment in each axis, a spring action is provided by each live hinge of the mount. The flexures can be machined with the adjustable plates biased closed, or an external temporary spring similar to a clothespin or large paperclip can be added. In addition, the flexures for the adjustable elements can be machined as separate pieces and then laser welded, screwed and glued, or otherwise fastened to the bases of the adjustable elements to connect the adjustable elements and thereby lower the cost of manufacture.
The design of this optical component mounting system is also configured to provide a fixed outer frame that is very rigid, for use in attaching the mounting to a laser system chassis. Adjustment screws for aligning the optical element fastened in the component mounting are located in the rigid outer frame for alignment stability.
By using live hinges created by machining slots in the material from which the optical component mounting is made, and locating them on two orthogonal lines radiating from the optical axis, the angular adjustments of the optical component in the mounting are made independent of each other. Thus, the process of aligning the optical component in the mounting is simplified. As shown in FIG. 2, the reference to the X axis and Y axis refers to the coordinate system depicted and more particularly to the angular adjustments along the X axis and the Y axis, more particularly, a xcex8X and xcex8Y adjustment. For convenience, the reference to the X axis and the Y axis herein relate to the angular xcex8X and xcex8Y adjustment
An object of the invention is a mounting apparatus for mounting an optical element such that the optical axis of the optical element is substantially aligned with corresponding elements in an optical system. The apparatus comprises a mounting body with a first section and a second section separated by a gap and coupled by a live hinge, wherein the first section and the second section have a hinged end at the live hinge and a free end opposing the hinged end, and wherein the first section has an optical receptacle for securing the optical element. There is an adjusting means for changing the gap between the first section and the second section at the free end, thereby adjusting an angular alignment in a first direction. A spring means is coupled to the first section and the second section, thereby providing resistance to increasing the gap. Finally, there is a locking means coupled to the first section and the second section securing the angular adjustment with a contact force substantially perpendicular to the first direction.
An object includes the mounting apparatus, wherein the locking means is a pair of plates secured proximate the free end, and wherein the plates extend across the gap and are secured to the first section and the second section. Additionally, the adjusting means is a screw threaded through the first section and contacting the second section.
Another object includes the live hinge being a remaining portion of the mounting body and the gap is a slot between the first section and the second section. Alternatively, wherein the live hinge is a portion of flexural material secured at the hinged end between the first section and the second section
It should be understood that the mounting apparatus accommodates an optical element which is selected from the group comprising: a lens, a mirror, a single optical fiber, an optical fiber bundle, a grating and a prism.
Yet a further object includes the spring means being selected from the group comprising: an external spring mounted across the gap at the free end, a clamp structure clamped across the gap, and an inward bias force introduced by a width of the gap being less at the free end and larger at the hinged end.
An object of the invention is a two axis gimbal mounting structure for alignment of an optical element, comprising a housing having a base plate, a middle plate and a front plate. The base plate and middle plate are separated by a first slot and coupled by a first flexible hinge at a first hinge end, and the middle plate and the front plate are separated by a second slot and coupled by a second flexible hinge at a second hinged end. The optical element mount to the front plate. There is a first means for angularly adjusting a first axis of the optical element by changing a gap dimension of the first slot at an adjusting end opposing the first hinge end. There is also a second means for angularly adjusting a second axis of the optical element by changing a gap dimension of the second slot at an adjusting end opposing the second hinge end. In addition, there is a first locking mechanism sandwiching the base plate and the middle plate using a force perpendicular to the first axis, and a second locking mechanism sandwiching the middle plate and the front middle plate using a force perpendicular to the second axis. The two axis gimbal mounting structure uses the first adjusting means to align the first axis of the optical element and the second adjusting means is used to align the second axis of the optical element. In a preferred embodiment, the first axis and the second axis are approximately perpendicular. An additional aspect of the two axis gimbal mounting structure is the inward spring bias of the first slot and the second slot to maintain an opposing resistance to changing the gap dimension.
A further object of the two axis gimbal mounting structure is a removeable alignment mechanism that is secured across the adjusting end used by the first and second means for angularly adjusting the respective first and second axis.
An additional object of the first means for angularly adjusting the first axis is an elongated member threadably engaging the middle plate and contacting the base plate thereby altering the gap dimension of the first slot. Also, the second means for angularly adjusting the second axis is an elongated member threadably engaging the front plate and contacting the middle plate thereby altering the gap dimension of the second slot.
An object of the invention is an apparatus for mounting an optical element with a corresponding optical axes aligned with an optical axes of other elements in an optical system, the apparatus comprising a unitary housing having a base section, a middle section and a front section, each section substantially parallel and coupled to each other by two small sections. The first small section forming a first live hinge between the base section and the middle section having a first free end opposing the live hinge. There is a second live hinge between the middle section and the front section with a second free end opposing the second live hinge. Each section is substantially separated from each other by a respective first and second gap, wherein the first and second gap is formed from narrow slots extending substantially through the housing leaving the respective small sections. The first live hinge allows adjustment along a first axis and the second live hinge allows adjustment along a second axis. In a preferred embodiment the first and second axis are substantially orthogonal. There is a first adjustment member threadably interconnecting the middle section and contacting the base section thereby altering the first gap and adjusting along the first axis. There is also a second adjustment member threadably interconnecting the front section and contacting the middle section thereby altering the second gap and adjusting along the second axis. The device includes a first pair of locking plates oriented on each side end of the base section and the middle section proximate the first free end. The first pair of locking plates is used for bridging the first gap and locking the base section to the middle section with a force substantially orthogonal to the first axis. A second pair of locking plates is oriented on each side end of the middle section and the front section proximate the second free end. The second pair of locking plates is used for bridging the second gap and locking the middle section to the front section with a force substantially orthogonal to the second axis. Finally, there is an optical receptacle on the front section for securing the optical element.
Another object includes where the first and second pair of locking plates have a central flexure section. The central flexure section of the locking plates allows the plates to have some flexibility in the direction of the clamping force. The flexure has no impact on the structural integrity once the plates are locked into place.
An additional object is the first and second pair of locking plates using a locking bolt extending from the first and second pair of locking plates through a hole in the middle and front sections respectively, with a corresponding nut on the respective opposing first and second pair of locking plates. Included as a variation is where the hole is oversized that allows a securing bolt to cleanly pass through the plates without contact.
And a further object is the apparatus for mounting, wherein the first adjustment member and the second adjustment member are removed from contact with the respective base section and the middle section after alignment.
In addition, further comprising a threaded insert engaging the adjustment member, wherein the insert is a dissimilar material form the adjustment member.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us on carrying out our invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.